Bis(ethylenedithio)tetrathiafulvalene Radical Salts with Anderson Type

Bis(ethylenedithio)tetrathiafulvalene Radical Salts with Anderson Type Heteropolymolybdates Containing Tris(alkoxo) Ligands Cai-Ming Liu,*,† Yong-Hong Huang,†,‡ De-Qing Zhang,*,† Song Gao,§ Feng-Chi Jiang,‡ Jian-Ying Zhang,† and Dao-Ben Zhu*,†

CRYSTAL GROWTH & DESIGN 2005 VOL. 5, NO. 4 1531-1538

Center for Molecular Science, Institute of Chemistry, Organic Solids Laboratory, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China, Chemistry Department, Jiangxi Normal University, Nanchang 330027, People’s Republic of China, and State Key Laboratory of Rare Earth Materials and Applications, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, People’s Republic of China Received January 6, 2005;

Revised Manuscript Received March 16, 2005

ABSTRACT: Anderson type heteropolymolybdates containing tris(alkoxo) ligands {MnMo6O18[(OCH2)3CR]2}3- (R ) -CH2OH, -CH2CH3, and -NH2) have been successfully utilized as anions to generate the bis(ethylenedithio)tetrathiafulvalene (ET) radical cation salts: (ET)5{MnMo6O18[(OCH2)3CCH2OH]2} (5H2O) 1, (ET)5{MnMo6O18[(OCH2)3CCH2CH3]2}‚(2CH3CN) 2, and (ET)6{MnMo6O18[(OCH2)3CNH2]2}‚(2CH2Cl2) 3. Compound 1 shows a metallic conducting property, but compound 2 presents semiconducting behavior although both compounds possess β′′ phase packing of ET molecules, while ET molecules in compound 3 exhibit R′′′ phase packing. Introduction Radical cation salts of the organic π-electron donor tetrathiafulvalene (TTF) and its ramification or analogue have been a focus of materials chemistry research since the discovery of superconductivity in organic materials.1-9 Organic π-electron donor radical cation salts with polyoxometalates as anions have attracted much attention2a since Ouahab et al. reported the first such compound consisting of TTF and the one electron reduced phosphotungstate Keggin anion [PW12O40]4- in a stoichiometry of 6:1 in 1988.2b The motivation rests with the polyoxometalates’ variability of charges, shape, and sizes, which can induce new organic packing and new physical properties. Many π-electron donor radical cation salts of simple polyoxometalates have been explored.2-5 The successfully utilized polyoxometalate anions include Lindqvist type [M6O19]2- (M ) MoVI, WVI), Keggin type [Xn+M12O40](8+n)- [Xn+ ) SVI, PV, SiIV, FeIII, BIII, 2(H+), CoII, CuII, ...; M ) MoVI, WVI], DawsonWells type [P2W18O62]6-, octamolybdate β-[M8O26]4-, and so on.2-6 However, only a few radical cation salts of polyoxometalate showing good metallic conductivity have been reported so far.8 Most of bis(ethylenedithio)tetrathiafulvalene (ET) radical cation salts of polyoxometalates are semiconductors or exhibit transitions to a semiconducting state at high temperatures;2 for example, radical cation salts (ET)11[P2W18O62]‚3H2O,6a (ET)11[ReOP2W17O61]‚3H2O,6b and (ET)5[VW5O19]‚6H2O6c show metal-like behavior at above 250 K, and compound β′′-(ET)5[H3V10O28]‚4H2O exhibits a metallic regime that disappears at as low as 50 K.9 An alternative approach is utilizing polyoxometalates containing organic groups as anions to construct ET radical cation salts. Such polyoxometalates possess improved solubility in organic solvents, favoring the * To whom correspondence should be addressed. E-mail: cmliu@ iccas.ac.cn, [email protected], and [email protected]. † Institute of Chemistry. § Jiangxi Normal University. ‡ Peking University.

growth of single crystals of radical cation salts with an electrocrystallization method. More importantly, the organic groups in polyoxometalates can be modified easily at the molecular level, and the organic π-electron donor packing and the conducting properties of the corresponding radical cation salts, therefore, can be modulated too. In this regard, we have used here the Anderson type heteropolyoxoanions containing tris(alkoxo) ligands {MnMo6O18[(OCH2)3CR]2}3- (R ) -CH2OH, -CH2CH3, and -NH2). These anions exhibit B type Anderson structures, in which six MoO6 octahedra share edges to form a hexagon around one MnO6 octahedron and six triply bridging oxygen atoms surrounding the MnIII center from two (OCH2)3CR residues.10 By electrochemical oxidation of ET in the presence of [N(C4H9)4]3{MnMo6O18[(OCH2)3CR]2}, we have obtained crystals of three ET radical salts with Anderson type heteropolymolybdates containing tris(alkoxo) ligands: (ET)5{MnMo6O18[(OCH2)3CCH2OH]2}‚ 5H2O 1, (ET)5{MnMo6O18[(OCH2)3CCH2CH3]2}‚2CH3CN 2, and (ET)6{MnMo6O18[(OCH2)3CNH2]2}‚2CH2Cl2 3. Compounds 1-3 represent the first examples of ET radical salts with Anderson polyoxometalates containing organic groups. Experimental Section Syntheses. BEDT-TTF was obtained by the method of ref 11 and recrystallized twice from chloroform. [N(C4H9)4]3[MnMo6O18{(OCH2)3CCH2OH}2] was prepared by literature method10 and recrystallized from DMF/ether. [N(C4H9)4]3[MnMo6O18{(OCH2)3CCH2CH3}2] and [N(C4H9)4]3[MnMo6O18{(OCH2)3CNH2}2] were synthesized in a similar way, but (HOCH2)3CCH2CH3 or (HOCH2)3CNH2 instead of (HOCH2)3CCH2OH]2 was used. Elemental analyses confirmed the purity of the starting materials. Electrochemical crystal growth was carried out in conventional U-shaped cells with Pt electrodes at room temperature over 2 weeks at a current of 0.5 µA. Each cell contained 10 mg of BEDT-TTF and 20 mg of [N(C4H9)4]3[MnMo6O18{(OCH2)3CCH2OH]2} in 50 mL of MeCN for 1 or 20 mg of [N(C4H9)4]3[MnMo6O18{(OCH2)3CCH2CH3]2} in 50 mL of MeCN for 2 or 20 mg of [N(C4H9)4]3[MnMo6O18{(OCH2)3CNH2]2} in 50 mL of CH2Cl2 for 3. After several days, very

10.1021/cg050004l CCC: $30.25 © 2005 American Chemical Society Published on Web 04/27/2005

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Table 1. Crystallographic Data and Structure Refinement for Compounds 1-3

a

identification

1

2

3

chemical formula formula weight crystal system space group a (Å) b (Å) c (Å) R (°) β (°) γ (°) V (Å3) Z T (K) λ(Mo KR) (Å) Fcalcd (g cm-3) µ(Mo KR) (mm-1) R1a [I > 2σ(I)] wR2b [I > 2σ(I)] S

C60H58MnMo6O31S40 3188.04 triclinic P1 h 9.427(2) 12.546(3) 22.514(5) 99.53(3) 100.79(3) 99.37(3) 2527.4(10) 1 150 (2) 0.71073 2.095 1.742 0.0487 0.1067 0.675

C60H50MnMo6N2O24S40 3096.00 triclinic P1 h 9.358(2) 12.783(3) 22.492(4) 99.36(3) 100.82(3) 101.07(3) 2537.9(9) 1 150 (2) 0.71073 2.026 1.727 0.0657 0.1463 0.727

C70H70Cl4MnMo6N2O24S48 3634.54 triclinic P1 h 9.0712(18) 15.977(3) 21.698(4) 70.01(3) 84.35(3) 88.29(3) 2940.8(10) 1 150 (2) 0.71073 2.052 1.732 0.0977 0.1562 0.975

R1 ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) ∑{[w(Fo2 - Fc2)2]/∑[wFo2]2}1/2. Table 2. Selected Bond Distances (Å) and Angles (deg) for Compound 1a bond distances Mn(1)-O(12) Mn(1)-O(10) Mo(1)-O(9) Mo(1)-O(8) Mo(1)-O(10)#1 Mo(2)-O(2) Mo(2)-O(8) Mo(2)-O(10)#1 Mo(3)-O(5) Mo(3)-O(12) Mo(3)-O(11)#1 S(3)-C(3) S(4)-C(4) S(5)-C(7) S(6)-C(8) C(7)-C(8) S(11)-C(13) S(12)-C(15) S(13)-C(16) S(14)-C(16) C(17)-C(18) S(20)-C(25) C(23)-C(24)

1.916(7) 2.122(6) 1.722(7) 1.933(7) 2.260(6) 1.723(7) 1.905(7) 2.277(7) 1.714(7) 2.383(6) 2.326(7) 1.768(9) 1.761(11) 1.752(10) 1.750(10) 1.343(13) 1.744(9) 1.729(10) 1.724(10) 1.723(11) 1.326(13) 1.738(9) 1.355(14)

O(12)#1-Mn(1)-O(12) O(12)-Mn(1)-O(11)#1 O(11)#1-Mn(1)-O(11) S(3)-C(5)-S(4) S(12)-C(15)-S(11) C(13)-S(11)-C(15) C(16)-S(14)-C(18) C(25)-S(19)-C(23)

180.0(5) 87.2(3) 180.0(4) 115.8(6) 113.6(6) 95.1(5) 95.1(5) 95.7(5)

Mn(1)-O(11) Mo(1)-O(3) Mo(1)-O(1) Mo(1)-O(11) Mo(2)-O(4) Mo(2)-O(6) Mo(2)-O(12) Mo(3)-O(7) Mo(3)-O(6) Mo(3)-O(1)#1 S(3)-C(5) S(4)-C(5) S(5)-C(6) S(6)-C(6) C(3)-C(4) C(15)-C(16) S(11)-C(15) S(12)-C(14) S(13)-C(17) S(14)-C(18) S(19)-C(25) S(20)-C(24) C(25)-C(25)#2

1.924(6) 1.690(7) 1.885(7) 2.400(6) 1.704(7) 1.903(6) 2.380(6) 1.713(6) 1.923(7) 1.950(7) 1.709(11) 1.750(10) 1.719(10) 1.740(11) 1.339(13) 1.347(13) 1.766(11) 1.754(10) 1.768(9) 1.761(9) 1.706(10) 1.752(10) 1.392(18)

O(12)#1-Mn(1)-O(10) O(12)-Mn(1)-O(11) O(11)-Mn(1)-O(10) S(5)-C(6)-S(6) S(14)-C(16)-S(13) C(16)-S(13)-C(17) S(19)-C(25)-S(20) C(25)-S(20)-C(24)

86.9(3) 92.8(3) 93.1(2) 115.7(6) 115.7(6) 95.3(5) 116.4(5) 94.5(5)

bond angles

a

#1: -x - 2, -y + 1, -z; #2: -x - 2, -y, -z + 1.

thin platelike amber crystals of 1 and 2 as well as dark block crystals of 3 were obtained from corresponding cells. Structure Determination. Suitable single crystals 1-3 were selected for indexing and intensity data collections at 150(2) K on a Rigaku RAXIS RAPID IP imaging plate system with Mo KR radiation (λ ) 0.71073 Å). Cell parameters were obtained by the global refinement of the positions of all collected reflections. A total of 16250 reflections were collected in the range 0.94° < θ < 27.47° (-12 e h e 12, -16 e k e 16, -29 e l e 29), of which 10957 are unique (Rint ) 0.0805), and 3845 with I > 2σ(I) were used in the refinement of the structure of 1. A total of 11996 reflections were collected in the range 0.94° < θ < 27.48° (-12 e h e 12, -16 e k e 16, -29 e l e 29), of which 9257 are unique (Rint ) 0.1161), and 2762 with I > 2σ(I) were used in the refinement of the structure of 2. A total of 19645 reflections were collected in

the range 1.00° < θ < 27.48° (-11 e h e 11, -20 e k e 20, -28 e l e 28), of which 12854 are unique (Rint ) 0.1061), and 5781 with I > 2σ(I) were used in the refinement of the structure of 3. Empirical absorption corrections from Ψ scan were applied. All three structures were solved by direct method and refined by a full matrix least-squares technique based on F2 using SHELXL 97 program. All nonhydrogen atoms were refined anisotropically, and all hydrogen atoms but those in solvent water molecules, solvent MeCN molecules, or solvent CH2Cl2 molecules and in amino groups of 3 were allowed as riding atoms. Selected crystallographic data and structure determination parameters for compounds 1-3 are given in Table 1. Selected bond lengths and angles for 1-3 are listed in Tables 2-4. Electrical Conductivity. Temperature dependence of the dc conductivity over the range 2-300 K was carried out using

Bis(ethylenedithio)tetrathiafulvalene Radical Salts

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Table 3. Selected Bond Distances (Å) and Angles (deg) for Compound 2a bond distances Mn(1)-O(8) Mn(1)-O(6) Mo(1)-O(4) Mo(1)-O(8) Mo(2)-O(12) Mo(2)-O(9) Mo(2)-O(6)#1 Mo(3)-O(1) Mo(3)-O(5) Mo(3)-O(6)#1 C(5)-C(6) C(5)-S(4) C(4)-S(4) C(6)-S(6) C(8)-S(5) C(3)-C(4) C(15)-S(11) C(16)-S(13) C(17)-S(13) C(18)-S(14) C(14)-S(12) C(25)-S(20) C(24)-S(20) C(23)-S(19)

1.937(9) 2.120(11) 1.724(10) 2.351(10) 1.710(11) 1.908(10) 2.243(9) 1.703(10) 1.892(10) 2.305(10) 1.383(19) 1.726(16) 1.748(16) 1.737(16) 1.767(17) 1.37(2) 1.699(15) 1.743(16) 1.800(17) 1.784(16) 1.815(17) 1.758(16) 1.754(16) 1.750(16)

O(8)#1-Mn(1)-O(8) O(8)-Mn(1)-O(7) O(7)-Mn(1)-O(7)#1 O(7)-Mn(1)-O(6) O(8)-Mn(1)-O(6)#1 O(6)-Mn(1)-O(6)#1 S(6)-C(6)-S(5) S(19)-C(25)-S(20) C(5)-S(4)-C(4) C(15)-S(11)-C(13) C(16)-S(13)-C(17) C(24)-S(20)-C(25)

180.0(7) 91.9(4) 180.0(7) 91.9(4) 86.3(4) 180.0(8) 113.8(8) 115.5(7) 95.3(8) 95.9(7) 98.0(8) 94.5(7)

Mn(1)-O(7) Mo(1)-O(11) Mo(1)-O(9) Mo(1)-O(5)#1 Mo(2)-O(10) Mo(2)-O(2) Mo(2)-O(8) Mo(3)-O(3) Mo(3)-O(2) Mo(3)-O(7) C(5)-S(3) C(3)-S(3) C(6)-S(5) C(7)-S(6) C(7)-C(8) C(15)-C(16) C(15)-S(12) C(16)-S(14) C(17)-C(18) C(13)-S(11) C(13)-C(14) C(25)-S(19) C(23)-C(24) C(25)-C(25)#2

1.963(10) 1.716(11) 1.917(10) 1.950(10) 1.717(10) 1.935(10) 2.390(10) 1.708(10) 1.958(11) 2.426(10) 1.700(15) 1.763(15) 1.762(16) 1.814(15) 1.33(2) 1.354(19) 1.760(16) 1.786(16) 1.34(2) 1.746(15) 1.34(2) 1.711(15) 1.34(2) 1.37(3)

O(8)#1-Mn(1)-O(7) O(8)-Mn(1)-O(7)#1 O(8)-Mn(1)-O(6) O(7)#1-Mn(1)-O(6) O(7)-Mn(1)-O(6)#1 S(3)-C(5)-S(4) S(11)-C(15)-S(12) C(5)-S(3)-C(3) C(6)-S(5)-C(8) C(15)-S(12)-C(14) C(18)-S(14)-C(16) C(25)-S(19)-C(23)

88.1(4) 88.1(4) 93.7(4) 88.1(4) 88.1(4) 116.8(9) 116.3(8) 95.3(8) 96.3(8) 93.9(8) 96.5(7) 96.1(8)

bond angles

a

#1: -x, -y, -z; #2: -x, -y + 1, -z + 1.

the standard four-probe technique. Conductivity measurements were performed on several single crystals for each of the three salts that gave suitable single crystals. Contacts to the crystals were made by gold wires attached with silver paint.

Results and Discussion The exact stoichiometry of compound 1 was determined by refinement of the crystal structure. Compound

Figure 1. ORTEP view of the structure of 1, showing the atom-labeling scheme (50% thermal ellipsoids). All hydrogen atoms are omitted for clarity.

1 shows the stoichiometry 5:1 formed by ET and polyoxometalate, which is similar to that observed in ET salts of Lindqvist polyoxoanions (ET)5[VW5O19]‚ 6H2O6c and (ET)5[V2W4O19]‚5H2O.2 As shown in Figures 1 and 2, the crystal structure of 1 consists of alternated layers of Anderson polyoxometalate {MnMo6O18[(OCH2)3CCH2OH]2}3- anions and ET molecules in the c-axis direction. The Anderson polyoxometalate anions connect each other through hydrogen bonds between O13 and O2 or their symmetry equivalents (O13‚‚‚O2 2.838 Å) to generate an anion chain along a-axis, with the MnMn distance of 9.427(2) Å. Parallel polyoxometalate anion chains are arranged to form layers in the ab plane, with the shortest Mn-Mn distance of 12.546(3) Å. These inorganic layers are separated by a distance of 22.514(5) Å from each other. All crystallized water molecules occupy the sites defined by the polyoxoanions in the ab plane. There are three crystallographically independent ET molecules (labeled as A, B, and C in Figure 3), which are aligned along the [212] direction. The organic layers are formed by infinite parallel chains of ET molecules, which are distributed according to the sequence ...-B-A-C-A-B... All ET chains are equivalent and run along the [210] direction. There exist strong interchain interactions through the sulfur atoms of ET molecules, giving rise to an increase of the organic dimensionality from one to two, and the known β′′ phase is thus formed. The only reported example of polyoxometalate-containing ET radical salt showing the β′′ phase is β′′-(BEDT-TTF)5[H3V10O28]‚4H2O,9 while an-

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Table 4. Selected Bond Distances (Å) and Angles (deg) for Compound 3a bond distances Mn(1)-O(2) Mn(1)-O(1) Mo(1)-O(5) Mo(1)-O(4) Mo(1)-O(3) Mo(2)-O(10) Mo(2)-O(11) Mo(2)-O(2) Mo(3)-O(8) Mo(3)-O(11) Mo(3)-O(2) S(4)-C(5) S(3)-C(4) C(5)-C(6) S(5)-C(7) S(6)-C(8) C(15)-C(16) S(11)-C(14) S(12)-C(15) S(13)-C(16) S(14)-C(16) C(17)-C(18) S(19)-C(24) S(20)-C(23) S(21)-C(26) S(22)-C(26) C(27)-C(28)

1.943(8) 2.098(8) 1.710(9) 1.942(8) 2.428(8) 1.717(8) 1.918(8) 2.396(8) 1.723(9) 1.938(8) 2.349(8) 1.756(14) 1.756(14) 1.371(17) 1.763(13) 1.742(13) 1.386(17) 1.741(13) 1.714(13) 1.733(12) 1.749(13) 1.371(17) 1.740(13) 1.773(13) 1.728(13) 1.738(13) 1.373(18)

O(2)-Mn(1)-O(2)#1 O(2)-Mn(1)-O(3) O(3)#1-Mn(1)-O(3) O(2)#1-Mn(1)-O(1)#1 O(3)-Mn(1)-O(1)#1 O(2)#1-Mn(1)-O(1) O(3)-Mn(1)-O(1) S(3)-C(5)-S(4) C(5)-S(3)-C(4) C(6)-S(5)-C(7) S(12)-C(15)-S(11) C(15)-S(11)-C(14) C(24)-S(19)-C(25) S(19)-C(25)-S(20) C(26)-S(21)-C(28)

180.0(3) 92.9(3) 180.0(5) 92.9(3) 88.0(3) 87.1(3) 92.0(3) 115.6(8) 95.0(6) 94.5(6) 116.0(7) 94.6(6) 96.2(6) 114.6(7) 95.7(6)

Mn(1)-O(3) Mo(1)-O(9) Mo(1)-O(12) Mo(1)-O(1)#1 Mo(2)-O(6) Mo(2)-O(12) Mo(2)-O(1)#1 Mo(3)-O(7) Mo(3)-O(4)#1 Mo(3)-O(3)#1 S(3)-C(5) S(4)-C(3) C(3)-C(4) S(5)-C(6) S(6)-C(6) C(7)-C(8) S(11)-C(15) S(12)-C(13) C(13)-C(14) S(13)-C(18) S(14)-C(17) C(25)-C(26) S(19)-C(25) S(20)-C(25) S(21)-C(28) S(22)-C(27)

1.969(8) 1.707(8) 1.920(8) 2.293(8) 1.711(9) 1.915(9) 2.334(8) 1.703(9) 1.911(8) 2.346(8) 1.720(14) 1.761(13) 1.328(17) 1.757(13) 1.747(13) 1.336(16) 1.734(13) 1.736(13) 1.356(16) 1.730(14) 1.750(13) 1.384(17) 1.741(12) 1.742(13) 1.759(13) 1.746(13)

O(2)-Mn(1)-O(3)#1 O(2)#1-Mn(1)-O(3) O(2)-Mn(1)-O(1)#1 O(3)1-Mn(1)-O(1)1 O(2)-Mn(1)-O(1) O(3)#1-Mn(1)-O(1) O(1)#1-Mn(1)-O(1) S(6)-C(6)-S(5) C(5)-S(4)-C(3) C(8)-S(6)-C(6) S(13)-C(16)-S(14) C(15)-S(12)-C(13) C(25)-S(20)-C(23) S(21)-C(26)-S(22) C(26)-S(22)-C(27)

87.1(3) 87.1(3) 87.1(3) 92.0(3) 92.9(3) 88.0(3) 180.0(7) 114.7(7) 94.5(6) 95.5(6) 114.5(7) 95.7(6) 95.0(6) 116.4(8) 94.4(6)

bond angles

a

#1: -x + 2, -y + 1, -z.

other compound (ET)11[P2W18O62]‚3H2O,6a which is formed by ET molecules and Dawson-Wells polyoxometalate anions in a ratio 11:1, exhibits the β phase stacking of ET molecules. As in many other two-dimensional radical cation salts of ET,2-6,12 the intrastack distances (range from 3.829 to 4.008Å) are significantly longer than the interstack

Figure 2. Structure projection along the a direction of 1.

ones (range from 3.273 to 3.608Å). Interestingly, there are two types of strong intermolecular contacts between the ET molecule and the Anderson polyoxometalate cluster. The first occurs between the sulfur atom from ET molecules and the terminal oxygen atom of the Anderson polyoxoanions with the shortest S‚‚‚O distance of 2.802 Å. The other is a hydrogen bond between


Figure 3. Molecular packing of the organic part in 1 showing the strong interchain connections and the three different types of ET molecules (A, B, and C).

terminal oxygen atoms of the Anderson polyoxoanions and ethylene groups of the ET molecules (the shortest C‚‚‚O distance of 3.130 Å). Similar trends have also been


observed in other ET radical cation salts of polyoxoanions (ET)11[P2W18O62]‚3H2O,6a R2-(ET)8[PNi(H2O)W11O39]‚ 2H2O,5 and R3-(ET)8n[PNi(H2O)W11O39]n‚2nH2O.5 Compound 2 shows the same stoichiometry of ET and polyoxometalate (5:1) as compound 1. The structure of 2 is composed of alternating layers of organic donors and the inorganic Anderson anions in the ab plane too (Figures 4 and 5). It is noteworthy that the change of methanol groups by ethyl groups in Anderson polyoxoanions does not affect the stacking pattern of ET molecules obviously. As in the structure of 1, three crystallographically independent ET molecules (noted as A, B, and C in Figure 6) are stacked following the sequence ...ABCBA... to form a chain, which runs along the [210] direction. There are no intermolecular S‚‚‚S contacts shorter than the van der Waals distance (3.70 Å) between ET molecules within the chain stacks. The chains connect each other by short S‚‚‚S contacts (the shortest ones range from 3.408 to 3.598 Å) to generate an organic layer in the ab plane. The organic molecules of neighboring chains are also parallel, leading to a β′′ phase. The inorganic layers are formed by the Anderson polyoxometalate anions in the ab plane with the shortest Mn-Mn distances are the b and c unit cell parameters, respectively. Unlike in compound 1, there are no hydrogen bonds between Anderson polyoxometalate anions. All of the solvent MeCN molecules occupy


Figure 5. Structure projection along the a direction of 2.

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the sites defined by the anions, and there is a short N‚ ‚‚S contact (3.149 Å) between the solvent MeCN molecule and one ET molecule. As in structure 1, two strong intermolecular contacts between the organic layers and the inorganic layers play an important role in the construction of structure 1: one occurs between the sulfur atom of ET molecules and the terminal oxygen

Liu et al.

atom of the polyoxoanions with the shortest S‚‚‚O distance of 2.751 Å. The other is a hydrogen bond between terminal oxygen atoms of the polyoxoanions and ethylene groups of the ET molecules with the shortest C‚‚‚O distance of 3.154 Å. Compound 3 possesses a different stoichiometry of 6:1 formed by ET and polyoxometalate. The structure of 3 contains layers of ET organic donors separated by inorganic Anderson anion layers (Figures 7 and 8). The organic layers exhibit the R′′′ mode of packing in the ET molecules, which can be described as formed by fragments of the well-known R′ and β′′ phases.13 These layers are formed by two types of ET stacks (Figure 9) that are parallel to the a-axis. Three crystallographically independent molecules noted A, B, and C are present in the R′′′ phase. Stacks I and II are almost equivalent and belong to one type of ET stack. Both of them have an alternate arrangement of A and B, which form A-B dimers, running in a zigzag mode along the a-axis. The shortest intra- and interdimer S-S distances are 4.011 and 4.141 Å, respectively. Whereas the other type ET


Figure 8. Structure projection along the b direction of 3.



Figure 10. Thermal variation of the normalized resistance of 1 from 1.8 to 300 K.


stack (III) is formed by dimers of C molecules with the shortest intra- and interdimer S-S distances (3.940 and 4.314 Å, respectively). Furthermore, there exist extensive shortest S-S interchain contacts between chains I and II (from 3.299 to 3.683 Å), between chains I and III (range from 3.393 to 3.412 Å) as well as between chains II and III (range from 3.393 to 3.412 Å). The dihedral angle of A-B is only 3.1°, while the plane of C forms angles of 58.6 and 61.3° with planes A and B, respectively. To our knowledge, the R′′′ phase has been observed for the first time in the ET polyoxometalate family although two other ET radical salts (BEDTTTF)2Br1.3(∆I1.1(∆Cl0.6(∆ (∆ ) 0.1)12e and R′′′-(BEDTTTF)6[Pb3Br9PhClMe2CO]13 also show similar ET packing. The Anderson polyoxoanions form closed packed layers in the ab plane. Similar to compound 1, there are hydrogen bonds between nitrogen atoms and oxygen atoms of Anderson polyoxoanions (the shortest N‚‚‚O distance is 2.907 Å) in compound 3 to generate an anion chain along the a-axis with the Mn-Mn distance of 9.0712(18) Å. Polyoxometalate anion chains are arranged in parallel to form a layer in the ab plane, with the shortest interchain Mn-Mn distance of 15.977(3) Å. All solvent CH2Cl2 molecules occupy the sites defined by the anions. As in compounds 1 and 2, two important intermolecular contacts between the organic layers and the inorganic layers were found in structure of 3: The contact between the sulfur atom of ET molecules and the terminal oxygen atom of the polyoxoanions (the shortest S‚‚‚O distance of 2.998 Å) is a little weaker than that in compounds 1 and 2 (the shortest S‚‚‚O distances are 2.802 and 2.751 Å, respectively). The other contact is a hydrogen bond between terminal oxygen atoms of the polyoxoanions and ethylene groups of the ET molecules (the shortest C‚‚‚O distance of 3.139 Å). Conductivity measurements were carried out with the standard four-probe method in the best developed face (the ab plane) of a thin plate single crystal of compounds

Figure 11. Thermal variation of the normalized resistance of 2 from 50 to 300 K.

1 and 2. The room temperature conductivity σ of 1 is about 470 S cm-1. As shown in Figure 10, the normalized resistance of 1 continuously decreases with decreasing temperature. This behavior is characteristic of metallic conductors. This metallic behavior can be easily understood due to the mixed valence of the ET donors and the extensive short donor-donor contacts.6,9 Compound 1 shows metallic behavior from room temperature to very low temperature (reach at about 20 K). The abrupt slight increase in resistance near 20 K possibly represents one phase transition. The compound β′′(BEDT-TTF)5[H3V10O28]‚4H2O exhibits a metallic behavior too; however, this compound becomes a semiconductor at a temperature lower than 50 K.9 Another three polyoxometalate-containing ET radical salts (ET)11[P2W18O62]‚3H2O,6a (ET)11[ReOP2W17O61]‚3H2O,6b and (ET)5[VW5O19]‚6H2O6c also show “light” metallic regimes at above 250 K; however, some phase transitions happened when the temperature was decreased further: (ET)11[P2W18O62]‚3H2O and (ET)11[ReOP2W17O61]‚3H2O then became semiconductors6a,6b and (ET)5[VW5O19]‚ 6H2O insulator.6c The room temperature conductivity of compound 2 was measured to be 0.208 S cm-1, and the temperature dependence of the resistance of 2 is shown in Figure 11. From 280-100 K, the resistance varies very little. However, below 100 K, it obviously increases upon lowering the temperature further, typical of semiconducting behavior. The activation energy was estimated

1538


to be 0.03 eV for compound 2. Unfortunately, because the crystals of the compound 3 are blocks and too small to run conductivity measurement with the standard four-probe method successfully in our laboratory, conducting properties analyses were not performed for compound 3. It is difficult to explain the difference in the conductivity behavior (metallic and semiconducting properties) between 1 and 2 quantificationally because there are too many atoms in both compounds to calculate their energy bands with a general computer. However, from the viewpoint of structure, organic groups in polyoxometalates of the two compounds have a great impact on their conductivity behavior: the group -CH2OH in polyoxometalate of compound 1 can form a hydrogen bond with the terminal oxygen atom from a neighboring polyoxometalate anion to generate a supermolecular anion chain while the group -CH2CH3 in polyoxometalate of compound 2 cannot; consequently, the ET molecules in compound 1 are arranged more tightly than those in compound 2, as shown by the smaller cell volume of 1 with respect to 2 (each cell contains five ET molecules in both compounds). In other words, stronger intermolecular interactions among ET molecules are formed in compound 1, and better conductivity properties of compound 1 are thus expected.

Liu et al.

(2) (3) (4)

(5) (6)

Conclusions The successful preparation of 1-3 gives novel examples of assembling the interesting ET radical cation salts of polyoxometalates using electrochemical crystal growth methods. This study demonstrates that the polyoxometalates containing organic groups may also be utilized to construct ET radical cation salts acting as bulky polyoxoanions because of not only their improved solubility in organic solvents, which can favor growth of single crystals of radical salts in an U-shaped electrocrystallization cell, but also the possibility for investigation of the influence of organic groups in polyoxometalates on the packing of organic π-electron donors and their conducting properties.

(7) (8) (9) (10) (11) (12)

Acknowledgment. This work was supported by the National Natural Science Foundation of China (20201012 and 90101025), the Major State Basic Research Development Program of the People’s Republic of China (G2000077500 and 2001CB610507), and the Chinese Academy of Sciences. Supporting Information Available: CIF files of the compounds 1-3. This material is available free of charge via the Internet at http://pubs.acs.org.

References (1) (a) Ishiguro, T.; Yamaji, K. Organic Superconductors; SpringerVerlag: Berlin, 1990; Vol. 88. (b) Williams, J. M.; Ferraro, J. R.; Thorn, R. J.; Carlson, K. D.; Geiser, U.; Whang, H. H.; Kini, A. M.; Whangbo, M. H. Organic Superconductors

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CG050004L

Bis(ethylenedithio)tetrathiafulvalene Radical Salts with Anderson Type

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